The fundamental concept of “keeping up with the Sun” involves matching the rotational speed of the Earth directly beneath you. If you travel westward at the same speed the Earth spins eastward, you remain fixed relative to the Sun, thus experiencing a perpetual sunrise or sunset. Since the Earth is a sphere, the speed required for this constant twilight is not the same everywhere, making the calculation dependent on your location. The maximum speed is needed at the widest part of the globe, which is the equator.
Required Speed at the Equator
The maximum speed necessary to match the Earth’s rotation occurs at the equator, the largest circumference of the planet. To calculate this speed, one divides the equatorial circumference (approximately 24,901 miles or 40,075 kilometers) by the 24 hours required for one rotation. This calculation results in an approximate speed of 1,037 miles per hour (mph), or 1,670 kilometers per hour (km/h). If you were traveling westward at this exact speed on the equator, the Sun would appear to hang motionless on the horizon.
How Latitude Changes the Calculation
The speed required to keep pace with the Sun changes dramatically as one moves north or south from the equator toward the poles. The reason for this variability lies in simple geometry: the circumference of the circle a person travels decreases as the latitude increases, shrinking the distance that must be covered in the same 24-hour period. At any given latitude, the required speed can be determined by multiplying the equatorial speed by the cosine of that latitude’s angle. For instance, at 45 degrees latitude, the rotational speed is reduced to approximately 733 mph (1,180 km/h). A person standing at 60 degrees north would only need to travel at about 518 mph (834 km/h). At the North and South Poles, the rotational speed effectively becomes zero. Therefore, the farther one moves from the equator, the less speed is needed to remain in perpetual twilight.
Achieving the Speed in Practice
Sustaining a speed of over 1,000 mph (1,600 km/h) to match the Earth’s rotation requires highly specialized aircraft. For comparison, the cruising speed of a standard commercial passenger jet is typically around 550 to 600 mph, meaning it is incapable of matching the Earth’s rotation even at higher latitudes. The required velocity is well into the supersonic range, which is faster than the speed of sound, or Mach 1, which is approximately 761 mph at sea level.
The retired Concorde supersonic jet, which was one of the few commercial aircraft capable of sustained supersonic flight, could cruise at Mach 2.04, or about 1,354 mph (2,179 km/h). This speed would have been sufficient to keep pace with the Earth’s rotation at the equator, allowing for a perpetual sunset experience.
Maintaining such speeds presents significant challenges, including the massive fuel consumption required to overcome air resistance and the structural heating of the airframe. Furthermore, traveling at supersonic speeds generates a powerful pressure wave known as a sonic boom, making sustained flight over populated land areas impractical due to noise regulations. To “keep up with the Sun,” the aircraft must overcome the air’s movement relative to the ground, requiring continuous, extreme thrust to maintain the necessary high ground speed.